Are aliens harvesting the spin of stars?

One of the challenges of searching for technosignatures (i.e., signs that intelligent life somewhere in the universe has created technology) is understanding what to look for. Technology is a very broad area, and different types would show up as different features. One of the most commonly cited is a Dyson sphere, which attempts to encapsulate a star and capture its outgoing light to produce energy. But while we’ve looked for the mid-infrared waste heat these structures would produce for decades, we haven’t found a definitive instance of one. According to a new paper, available as a preprint on arXiv by Turkish high school student Sahin Torlakcik, that might be because we are looking for the wrong type of energy altogether.

In his paper, Torlakcik introduces the concept of stellar J-harvesting—building a system that could deliberately extract a star’s rotational angular momentum. To be clear, this solution wouldn’t capture the same energy output as a full Dyson sphere (or, more accurately, swarm), but it does have two massive advantages—it requires much less physical material to build, and it would generate waste heat millions of times lower than the star’s luminosity, essentially making it “invisible” to most infrared surveys.

So how would this work in practice? You can’t simply set up a frictional braking system on a star. Instead, you would have to sap its energy by using one of a few different electromagnetic coupling techniques.

According to the paper, one technique would be to build a massive conducting structure embedded in the solar wind that extracts angular momentum using Alfvén-wave coupling. These low-frequency oscillations of magnetic fields can interact with the tether, transferring some of the star’s angular momentum into the tether itself.

An alternative approach is to create what is essentially a giant orbital flywheel. Building a massive ring at approximately 1 AU (the distance from the Sun to Earth) could capture angular momentum from the star via Lorentz-force coupling. Using the Lorentz force, the fundamental force exerted on a charged particle by a magnetic field, this megastructure could scavenge angular momentum from the star by using its magnetic field to push on a massive electrically conductive ring.

Another interesting alternative is a synchrotron spin-down array. Synchrotron radiation is a form of radiation that occurs when a particle, such as an electron, travels a curved path near the speed of light. When these particles travel along a magnetic field line, they lose energy by emitting highly directional beams of radiation, known as synchrotron radiation.

By placing an array of extremely strong electrically conductive structures in the flow of the solar wind, this technosignature would accelerate those charged particles to near-relativistic speeds and thereby emit synchrotron radiation. Because Newton’s third law holds that every action has an equal and opposite reaction, this radiation has a reactive torque that pushes the array. Since the array is coupled to the star’s stellar wind, it opposes and slows the star’s rotation. Crucially, this technique would also emit a specific technosignature of its own, in the form of radio waves or X-rays, depending on the speed and field strength of the system.

Some of these techniques are similar to those seen in another technosignature idea—starlifting—whereby an advanced civilization intentionally harvests material from a star, either to use that material to build megastructures or to artificially extend the star’s life by lowering its mass. However, this particular use case has a very distinct pattern that we can easily search for—stars that are rotating more slowly than their peers.

So Torlakcik began that search himself. He selected the Kepler field of stars for a first look and sorted the stars by color and surface gravity while also applying strict filters to eliminate natural false positives (like subgiants and pre-main-sequence stars). He was left with a dataset of 6,725 FGK main-sequence stars. Out of this group, two interesting candidates emerged—KIC 67606183 and KIC 9834255. Both are G-type main-sequence stars but have relatively slow rotation periods of 61 and 65 days, respectively, compared with the 5–10 days that stars their age normally take to rotate.

To be clear, Torlakcik does not claim to have found a rotational-sapping megastructure at these two locations. In fact, their slow rotation rates are likely due to some other mundane astrophysical phenomenon, such as an unresolved binary or low metallicity. But at the very least, maybe it’s worth a look at these two stars in particular to see if we can figure out why, exactly, they are rotating so much more slowly than their peers.

Time for more observations, then, and Torlakcik has several ideas for follow-up studies that could help narrow the search for hints of these types of megastructures in the future. Luckily, he will have a long time to continue that search. After all, he’s only in high school and already starting to make a name for himself in the search for technosignatures.

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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